自定义回调中的Flutter小部件返回值

我创造了自己的 Widget 其中包括 DatePicker ,这里是代码:

class DatePicker extends StatelessWidget {
  final Icon icon;
  final DateTime initialDate;
  final ValueChanged<DateTime> onDateSelected;

  DatePicker({this.icon = const Icon(Icons.date_range), @required this.initialDate, this.onDateSelected});

  Future<Null> _selectDate(BuildContext context) async {
    final DateTime picked = await showDatePicker(context: context, initialDate: initialDate, firstDate: DateTime(2015, 8), lastDate: DateTime(2101));
    if (picked != null && picked != initialDate) {
      // TODO: return the picked value in the 'OnDateSelect' callback
      print(picked.toString());
    }
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      children: <Widget>[
        Text(initialDate.toString()),
        IconButton(
          icon: this.icon,
          onPressed: () => _selectDate(context),
        )
      ],
    );
  }
}

我想这样使用它:

DatePicker(
      initialDate: _ticketDate,
      onDateSelected: (newDate) {
        print(newDate);
      },
    );

我不知道的是如何返回在自定义中选择的日期 onDateSelected 回拨一次 Future<Null> _selectDate 已经被处决。

有什么想法吗?